1. Field of the Invention
The invention relates to a method for verifying the correct transport of steel material, for example banknotes, particularly in an automatic cash dispenser. Furthermore, the invention relates to a device for carrying out the method.
2. Description of the Prior Art
In the case of a known automatic cash dispenser, banknotes are dispensed individually one after the other from the banknote cartridges until the amount desired by the customer is reached. During this dispensing, it is possible for a number of banknotes to be transported lying one on top of the other, which would lead to incorrect dispensing. The automatic cash dispenser therefore contains devices which detect the multiple transport of banknotes and segregate the incorrect banknotes or the bundle of banknotes.
Patent Document No. 38 16 943 discloses a method of testing sheet material by sensing the sheet material with radiation along a predetermined sensing path. The sensing takes place under the transillumination principle. On the transmission side, light-emitting diodes are subjected to a current from a controllable current source, and on the receiver side photodiodes determine the light passing through the sheet material. If a number of sheets lie one on top of the other, the signal of the photodiode drops below a predetermined limit value, and incorrect transport fo the sheet material is signaled. The set current is made up of a basic current value and a differential current value. The differential current value is determined on the basis of sample sheets in a calibrating operation. The basic current value is set such that on the receiver side the signal level lies within a predetermined measuring range.
The principle described in German Patent Document No. 38 16 943 therefor, in which current control is used and the signal level of the detector is monitored within predetermined limits, has proven successful in practice. If, however, sheet material with greatly varying transillumination properties is used, for example American dollar bills, the reliability of the determination of multiple transport of sheet material may be restricted.
German Patent Document No. 93 10 528 therefor; discloses a paper-thickness measuring device which contains a mechanical sensor. The sensor contains a sensor coil through which current flows and the impedance of which changes when an element enters its magnetic field. The depth of entry depends on the thickness of the paper. Furthermore, German Patent Document No. 33 00 320 therefor; and German Patent Document No. 37 05 304 therefor describe the use of inductive displacement pickups for measuring the thickness of paper sheets.
European Application 0 405 466 therefor; discloses a method and a device according to the preambles of claims 1 and 8. According to this document, a Hall generator is arranged lying opposite a fixedly arranged permanent magnet, so that an air gap is formed. A magnetically conducting end of a touching lever engages in this air gap and changes the magnetic field in a manner dependent on the deflection of the touching lever. This change in the magnetic field is determined by the Hall generator, the signal of which is evaluated for determining correct transport of sheet material.
WO-A-86/00160 discloses a thickness-measuring device for banknotes. Situated opposite a Hall generator is a permanent magnet. A that is fed into the device banknote increases the distance between the permanent magnet and the Hall generator, so that a magnetic field change is produced, whereupon the resistance of the Hall generator changes. The setting of a control current for the Hall generator dependent on the type of banknote and the interaction with the sensitivity of the arrangement of the permanent magnet and Hall generator are not described in this document.